Carbon nanotubes are hexagonal networks of carbon atoms forming seamless tubes with each end capped with half of a fullerene molecule. Presently, there are three main approaches for the synthesis of single- and multi-walled carbon nanotubes. These include the electric arc discharge of graphite rod (Journet et al. Nature 388: 756 (1997)), the laser ablation of carbon (Thess et al. Science 273: 483 (1996)), and the chemical vapor deposition of hydrocarbons (Ivanov et al. Chem. Phys. Lett 223: 329 (1994); Li et al. Science 274: 1701 (1996)). Multi-walled carbon nanotubes can be produced on a commercial scale by catalytic hydrocarbon cracking while single-walled carbon nanotubes are still produced on a gram scale. Present methods produce both single-walled and multi-walled carbon nanotubes, as well as other contaminants, and purification of SWNTs can be time consuming and expensive.
Generally, single-walled carbon nanotubes are preferred over multi-walled carbon nanotubes because they have unique mechanical and electronic properties. Defects are less likely to occur in single-walled carbon nanotubes because multi-walled carbon nanotubes can survive occasional defects by forming bridges between unsaturated carbon valances, while single-walled carbon nanotubes have no neighboring walls to compensate for defects. Defect-free single-walled nanotubes are expected to have remarkable mechanical, electronic and magnetic properties that could be tunable by varying the diameter, and chirality of the tube.
A method for the production of SWNTs is disclosed in U.S. Pat. No. 6,764,874 to Ruth Zhang et al. using thin nickel film, Fe/Co or Fe/Ni as the catalyst. In addition, PCT Publication No. WO 06/050903 to Sigurd Buchholz et al. discloses the use of Fe:Mo catalyst and the use of hydrogen gas in order to generate the catalyst. These method can not produce SWNTs on a commercial scale, and the quality of the SWNTs can be low.
The methods described above still produce significant by-products and/or low yields of SWNTs. Thus, there is a need for methods and processes for controllable synthesis of high quality carbon single walled nanotubes. Accordingly, the present invention provides novel methods and processes for the synthesis of high quality SWNTs.